Apparatus for determining the temperature of tobacco



Marh 24, 1970 w. WOCHNOWSKI 3,502,085

APPARATUS FOR DETERMINING THE TEMPERATURE OF TOBACCO Filed Feb. 21, 1967 2 Sheets-Sheet 1 Fig. 1

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206 l 2071 i: A 1% 24kg? 224 205 zzz 210 204 INVENTOR.

March 24, 1970 W. WOCHNOWSKI APPARATUS FOR DETERMINING THE TEMPERATURE OF TOBACCO Filed Feb. 21, 1967 2 Sheets-Sheet 2 Tem q 2 9 6 115:

' 16 2'0 3o so 6 0 ($ec "7/36' Fig i 100 I l 1 5 fo r {(min) 45 I l 2I3 I l I Tenn 2 I I I I I 7 0 I I 16 (min) I I I l I I, 15 35 2'3 6, INVENTOR.

United States Patent 3,502,085 APPARATUS FOR DETERMINING THE TEMPERATURE OF TOBACCO Waldemar Wochnowski, Hamburg-Volksdorf, Germany,

assignor to Hauni-Werke Korber & Co. KG., Hamburg-Bergedorf, Germany Filed Feb. 21, 1967, Ser. No. 617,618

Claims priority, application Germany, Mar. 12, 1966,

H 58,78 Int. Cl. A24b 9/00, 3/04, 3/10 U.S. Cl. 131-135 11 Claims ABSTRACT OF THE DISCLOSURE Background of the invention The present invention relates to apparatus for determining the temperature and/or the moisture content of fibrous materials, particularly for determining the temperature and/or moisture content of tobacco which is conveyed in the form of a continuous stream or layer each unit length of which contains substantially the same quantity of whole or comminuted tobacco leaves.

In modern tobacco processing plants, it is often necessary to heat tobacco to a predetermined elevated temperature and to thereupon cool the tobacco to a predetermined lower temperature. For example, expulsion of nitrogen from Burley tobacco normally involves heating successive increments of a travelling tobacco stream to a temperature which is high enough to insure expulsion of nitrogen, and the thus heated tobacco stream is thereupon cooled to a temperature which is desirable in further processing of tobacco. Furthermore, tobacco is often heated for the sole purpose of expelling surplus moisture, and such heating is normally followed by a cooling treatment, preferably by contact with a current of cool gas. Satisfactory cooling and/or heating of tobacco involves accurate determination of temperature, for example, immediately upon completion of the heating operation, so that the operators can calculate and regulate the quantities of coolant which are necessary to reduce the temperature of tobacco to a desired value. Accurate determination of the moisture content is of equal importance because certain treatment can be carried out in a satisfactory manner only if the tobacco contains a predetermined minimum amount of moisture.

Many heretofore known temperature measuring de vices and apparatus for determination of moisture content are either inaccurate, too bulky, too complicated and/or too expensive. As a rule, such known devices and apparatus comprise detectors which must be placed in direct contact with the body of tobacco and, being unable to contact all zones of a batch or layer of tobacco leaves or shreds, the results of their measurements are often misleading. Furthermore, the heat absorbing capacity of many conventional detectors is much higher than the heat absorbing capacity of tobacco, and this is another factor that affects their accuracy. It was found that presently known detectors which are used to determine the temperature and/ or moisture content of tobacco are particu- 3,502,085- Patented Mar. 24, 1970 larly ineffective when the tobacco is in motion, especially if the tobacco is conveyed in the form of a relatively thick and wide layer to insure processing at a desired rate required in modern mass-processing tobacco plants.

Accordingly, it is an important object of the present invention to provide a novel and improved apparatus for determining the temperature and/ or moisture content of successive increments or unit quantities of tobacco at a rate of speed which is necessary in a modern tobacco processing plant and with a degree of accuracy which is unmatched by the presently known apparatus.

Another object of the invention is to provide an apparatus wherein the determination of temperature and/ or moisture content of successive unit quantities of tobacco is incidental to other treatments to which the tobacco is subjected during processing so that such determination of temperature and/or moisture content does not consume any extra time and/ or space.

A further object of the invention is to provide an apparatus for determining the temperature (and hence the moisture content) of heated tobacco with means for utilizing the results of such determination for proper heating and/or cooling of successive increments of a travelling tobacco mass.

An additional object of the invention is to provide an apparatus for accurately determining the average temperature of a relatively large or relatively small unit quantity of tobacco or like fibrous material.

A concomitant object of the invention is to construct and assemble the apparatus in such a way that it preferably performs at least one additional useful function so that the additional function is incidental to accurate determination of the temperature and/or moisture content, or vice versa.

Still another object of the invention i to provide an apparatus which can accurately determine the average temperature of successive batches of tobacco without necessitating bodily contact of tobacco particles with the testing and/or detecting devices.

An ancillary object of the invention is to provide a machine for varying the temperature of Burley tobacco which embodies the above outline apparatus and wherein such apparatus can regulate the temperature of successive increments of tobacco with a very high degree of accuracy.

Summary of the invention My invention resides in the provision of an apparatus for determining the temperature and/or the moisture content of tobacco, especially nitrogen-rich Burley tobacco. The apparatus comprises means for conveying a stream of tobacco at a substantially constant rate, means for passing a current of gas transversely through the tobacco stream so that tobacco exchanges heat with the gas, and means for determining a change in a given physical property of the gas, preferably the differential in temperatures of gas prior and subsequent to exchange of heat with tobacco, by measuring the gas temperature at least subsequent to (but preferably prior and subsequent to) such exchange of heat. The tobacco stream is preferably advanced in the form of a layer, and the amounts of gas passing through the layer are preferably regulated, for example, by utilizing one or more adjustable fans which are arranged to blow or to draw gas through the tobacco stream.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

Brief description of the drawing FIG. 1 is :a longitudinal vertical section through an apparatus which embodies one form of the present invention;

FIG. 2 is a fragmentary longitudinal vertical section through a second apparatus;

FIG. 3 is a fragmentary longitudinal vertical section through a third apparatus;

FIG. 4 is a diagram showing the manner in which the temperature and moisture content of tobacco vary as a function of time during heating in the apparatus shown in FIG. 1, 2 or 3;

FIG. 5 is a diagram showing the manner in which the temperature and moisture content of tobacco vary if the apparatus includes an infrared radiation heater; and

FIG. 6 is a diagram showing the manner in which two tobacco streams are cooled in the apparatus shown in FIG. 1, 2 or 3.

Description of the preferred embodiments Referring first to FIG. 1, there is shown an apparatus for determining and regulating the temperature and moisture content of Burley tobacco. The apparatus comprises a conveyor 4 which is constituted by an endless foraminous belt and serves to advance a continuous stream 3 of tobacco in an elongated horizontal or nearly horizontal path. The tobacco stream 3 forms on the upper stringer of the belt 4 a layer of at least nearly constant height and width. A feed, including an endless conveyor belt 2, serves to supply tobacco onto the upper stringer of the belt 4, and a take-off conveyor belt 12 receives properly treated tobacco from the right-hand end turn of the belt 4. During their travel with the upper stringer of the belt 4, successive increments or unit quantities of the tobacco stream 3 pass first through a heating zone in a drying chamber 6, thereupon through a cooling zone in a cooling chamber 8, and finally through a moistening or wetting zone in a wetting chamber 10. The three portions of the path in which successive increments of the tobacco stream 3 are subjected to heating, cooling and wetting actions are immediately adjacent to each other. The chambers 6, 8, are preferably assembled into a common housing which is provided with suitable openings for the upper and lower stringers of the belt 4 and for the tobacco stream 3.

The cooling chamber 8 forms part of a pneumatic unit 9 which serves to effect the passage of a current of air or other suitable gas transversely through successive increments of the tobacco stream 3 whereby the gas flows upwardly, first through the lower stringer and thereupon through the upper stringer of the belt 4. The drying chamber 6 forms part of a heating unit 11 which further includes a blower or fan 16 arranged to draw through the belt 4 an ascending current of hot gas (preferably air) whose temperature is high enough to effect expulsion of nitrogen from tobacco which forms the stream 3. The heating unit 11 further comprises a preferably electric heater 14 installed in a supply pipe 13 which furnishes gas into the interior of the chamber 6. The thus heated current of gas passes through the lower stringer of the belt 4, thereupon through the upper stringer and through the tobacco stream 3, and is evacuated through a discharge pipe which is connected to the suction side of the fan 16. The chamber 6 accommodates a plate-like sieve 20 which is disposed at a level below the lower stringer of the belt 4 and serves as a means for agitating and distributing the heated gas uniformly in all regions of the chamber 6 to effect uniform heating of the tobacco stream 3. The sieve 20 may be provided with circular, slot-shaped or otherwise configurated interstices or openings. Analogous interstices or openings are provided in the belt 4 to permit passage of hot gas through the tobacco stream 3.

The pneumatic unit 9 further comprises a supply pipe 22 which admits cool gas into the lower zone of the chamber 8, and such gas thereupon passes through the interstices of a lower sieve or distributor 30 which is disposed below the lower stringer of the belt 4 and insures uniform distribution of cool gas in each region of the chamber 8. The thus distributed cool gas then passes through the upper stringer of the belt 4 and tobacco stream 3 to exchange heat with successive increments of Burley tobacco. A further sieve 32 is disposed at a level above the tobacco stream 3 to insure that the upper portion of the chamber 8 receives a current of heated gas whose temperature is uniform in all zones thereof, and such gas is thereupon evacuated through a discharge pipe 26 which is connected to the suction side of a second blower or fan 33. The measuring means of the improved apparatus comprises two detectors 24, 28 which are respectively installed in the current of gas below the lower sieve 30 and above the upper sieve 32 so that the detector 24 determines the temperature of inflowing cool gas and the detector 28 determines the average temperature of gas which has exchanged heat with the tobacco stream 3 so that its temperature is higher that that of the gas which enters via supply pipe 22. The mounting of the detectors 24, 28 is preferably such that each thereof comes in contact with substantial amounts of flowing gas to insure that each of these detectors furnishes measurements which are truly representative of the gas temperature in the lower and upper portions of the chamber 8. The measurements furnished by the detectors 24, 28 are very accurate, and this is due to a considerable extent to the provision of sieves 30, 32 which agitate and distribute the gas current over the entire interior of the chamber 8.

The detectors 24, 28 are respectively connected with signal transmitting devices 46, 44 of known design which furnish signals to an evaluating device 48 whereby the intensity or another characteristic of each signal indicates the exact temperature of gas in the corresponding region of the chamber 8. The evaluating device 48 sends output signals which are indicative of the differential in temperatures of gas prior and subsequent to exchange of heat with the tobacco stream 3. The devices 44, 46, 48 form part of a control system 22 which further includes an adjusting device 27 serving to regulate the heating action of the heater 14 as a function of the differential in temperatures of gas prior and subsequent to exchange of heat with tobacco in the chamber 8. The control system 29 further includes a rated value selecting device 50 whose output signal is compared with the output signal of the evaluating device 48. When the two output signals are different, the adjusting device 27 receives a signal to intensify or weaken the heating action of the heater 14 upon the stream of gas flowing through the supply pipe 13, i.e., to intensify or to weaken the heating action of gas in the chamber 6 as a function of measurements carried out by the detectors 24 and 28.

The arrangement is such that, if the difference between the temperatures determined by the detectors 24, 28 exceeds the value indicated by the rated value selecting device 50, the adjusting device 27 reduces the heating action of the heater 14, and vice versa.

The Wetting chamber 10 forms part of a wetting or moistening unit 31 which further includes a blower or fan 38 connected to an outlet at the upper end of the chamber 10 and a supply pipe 40 which is connecetd with the lower part of the chamber 10 and admits atmospheric air or another gas. The inflowing gas is mixed with water or another moistening agent which is admitted in measured quantities through a feed conduit 41 and enters an atomizer 42. The chamber 10 also accommodates two sieves 34, 36 which are respectively installed below the lower stringer and above the upper stringer of the belt 4 and serve to distribute moisture-laden gas uniformly in all regions of the chamber 10. The amounts of moisture admitted to air flowing through the atomizer 42 are such that tobacco which leaves the chamber 10 is ready for processing at a further station which is not shown in FIG. 1.

The operation is as follows:

A continuous layer of stratified Burley tobacco is formed on the upper stringer of the belt 4 and enters the drying chamber 6 where it undergoes intensive heating action by a current of hot gas flowing from the pipe 13 to the suction side of the fan 16. The heating action of the heater 14 sufiices to insure that the current of ascending hot gas in the chamber 6 expels nitrogen from the tobacco stream 3. At the same time, the current of hot gas expels from tobacco a substantial percentage of moisture so that the tobacco must be moistened again in order to be ready for further processing at the station which receives tobacco from the take-01f conveyor belt 12.

The cooling chamber 8 receives successive increments of hot Burley tobacco, and such tobacco is cooled by exchange of heat with gas which is supplied by the pipe 22 and flows into the pipe 26. The average temperature of cool gas Which is admitted by the pipe 22 is measured by the lower detector 24. The upper detector 28 determines the average temperature of heated gas in the space above the sieve 32. The rate of gas inflow through the pipe 22 is selected in such a way that it remains in a given relationship to the rate of tobacco travel through the chamber 8. Therefore, the differential in gas temperatures determined by the detectors 24, 28 is an indication of the average temperature of successive increments of Burley tobacco in the chamber 8. Since the moisture of tobacco is directly related to its temperature, the aforementioned differential in temperatures is also indicative of the average moisture content of tobacco in the chamber 8. The output signals furnished by the signal transmitting devices 46, 44 are indicative of temperatures determined by the detectors 24, 28, and such signals are fed into the evaluating device 48. If the output signal of the device 48 matches the signal furnished by the rated value selecting device 50, the heating action of the heated 14 remains unchanged; otherwise, the heating action of the heater 14 is either intensified o-r weakened to insure that the heating action of the current of gas ascending in the drying chamber 6 is a function of the differential in temperatures determined by the detectors 24 and 28. It can be said that the heating action in the chamber 6 invariably depends from the rate value selected by the device 50.

Cooled Burley tobacco leaves the cooling chamber 8 and is conveyed across the wetting chamber 10 to have its moisture content raised prior to transfer onto the take-off conveyor belt 12.

In the apparatus of FIG. 1, the tobacco stream 3 is heated by a current of air which ascends in the drying chamber 6. The manner in which the temperature of tobacco rises is illustrated in FIG. 4. The temperature (in C.) is measured along the ordinate and the time (in minutes) is measured along the upper abscissa. The lower abscissa indicates the moisture content F of tobacco during successive stages of heating in the chamber 6. It is assumed that the upper stringer of the foraminous belt 4 supports 2 kilograms of dried tobacco per square meter, that the initial temperature of ascending gas current 111 the chamber 6 is 130 C., and that the suction fan 16 causes the ascending current to travel at a speed of 0.65 meter per second. FIG. 4 shows that, after an initial rise in temperature, the temperature of tobacco during the first nine minutes of heating remains substantially constant (about 60 C.). During this period of nine minutes, the moisture content of tobacco decreases from 45 to 10 percent. Thereupon, the temperature of tobacco rises rapidly and, after a total time of twelve minutes, reaches a temperature of between 110-115 C., while the moisture content drops to percent. The temperature thereupon remains unchanged and is slightly below the maximum temperature of ascending gas. Such behavior is due to the hygroscopic nature of tobacco. As is known, the temperature of Burey tobacco must be raised to a predetermined value to effect expulsion of nitrogen. In contrast to the above-described operation of the apparatus 6 shown in FIG. 1, the temperature of Burley in the chamber 6 can be raised much more rapidly by resorting to infrared radiation. For example, and as shown in the diagram of FIG. 5, tobacco entering the chamber 6 may be heated first by an ascending current of heated gas and, after six minutes of heating, passes a heating zone in which it undergoes heating action by infrared radiation (microwaves). After a total time of seven minutes and thirty seconds, the temperature of tobacco has been raised from 58 to 110 C., i.e., the temperature is high enough to bring about expulsion of nitrogen. At the same time, the moisture content of tobacco is reduced from 45 percent only to 18 percent, i.e., the moisture content is much higher than in the example which was described in connection with FIG. 4. This means that the wetting unit 31 can be dispensed with because a tobacco stream having a moisture content of about 18 percent is ready to undergo further processing without necessitating a moistening or wetting treatment. The manner in which an infrared heater can be installed in the drying chamber 6 of FIG. 1 is indicated by broken lines at 43. It will be seen that this heater 43 is installed in the downstream region of the space defined by the chamber 6 so that it heats tobacco which has been preheated by ascending air flowing from the pipe 13 to the suction side of the fan 16. FIG. 1 shows further (by broken lines) that the infrared heater 43 can be connected with the adjusting device 27 so that its heating action upon successive increments of the stream 3 may be varied in the same way as the action of the heater 14, i.e., as a function of the differential in temperatures determined by the detectors 24 and 28 in the chamber 8.

The changes in temperature of tobacco during travel through the cooling chamber 8 are illustrated in the diagram of FIG. 6. The abscissa indicates the time in seconds and the ordinate the temperature in C. The tWo curves indicate that the temperature of tobacco drops rapidly immediately after entry into the chamber 8 and that the drop in temperature is thereupon gradual. T herefore, and in order to regulate the heating action of gas in the drying chamber 6, it is advisable to measure the drop in temperature of that portion of the current of gas in chamber 8 which traverses the tobacco stream 3 immediately after entry of successive increments into the chamber 8. This Will be explained in more detail hereinafter.

The total dwell of successive increments of the stream 3 in chamber 8 is now assumed to be sixty seconds. The temperature of air entering via supply pipe 22 is 20 C., and the rate of gas flow is such that forty kilograms of gas are used to cool four kilograms of dried tobacco. The upper curve A indicates the rate at which the gas current cools a stream of tobacco whose initial temperature is 110 C. The temperature of tobacco leaving the chamber 8 is 30 C. The moisture content of tobacco is less than 5 percent. The curve B indicates the drop in temperature of tobacco whose initial temperature (on entry into the chamber 8) is C. The moisture content of tobacco in the second stream B is 8 percent and the temperature of such tobacco on leaving the chamber 8 has been reduced to 25 C.

The difference in temperatures of cooling gas can be calculated in accordance With the equation GINC'IHATT G .C

7 the curve A in FIG. 6), the temperature differential of cooling gas is 4-0.4-80 o AT 13.2 C.

If the initial temperature of tobacco is 90 C. (curve B in FIG. 6), the temperature differential of cooling gas is In this latter instance, the heating action of the heater 14 will be intensified until the temperature differential of cooling gas (T rises to 132 C.

The measurement is more accurate if the detectors 24, 28 determine the temperature of that portion of the ascending gas current in chamber 8 which is first to pass through successive increments of the tobacco stream 3. For example, it is now assumed that the detectors 24, 28 are active during the first ten seconds of cooling, i.e., during the interval when the first sixth of the total amount of cooling gas was caused to traverse the tobacco stream in the chamber 8. As shown in FIG. 6, after ten seconds of cooling the temperature of tobacco (curve A) is reduced from 110 C. to about 75 C. Thus, the temperature differential of cooling gas can be determined as follows:

AT -35.7 C.

If the initial temperature of tobacco is 90 C. (curve B in FIG. 6), the difierential in temperature of cooling gas after 10 seconds of cooling is as follows:

AT 25 C.

Thus, the apparatus which measures only during the first ten seconds of cooling is about four times as accurate as the apparatus which determines the temperature differential during the entire cooling period (sixty seconds).

Certain component parts of the apparatus shown in FIG. 1 can be utilized for determination of the temperature or moisture content of successive increments or batches of tobacco or other fibrous material independently of expulsion of nitrogen. Thus, in its elementary form, the apparatus of my invention must comprise only a conveyor or a feed for supplying tobacco, preferably in accurately measured unit quantities, into the chamber 8, a device for causing a current of air or another gas to flow through the batch of tobacco in the chamber 8, and detectors 24, 28 for determining the temperature of gas prior and subsequent to passage of such gas through the tobacco. If the initial temperature of gas is identical with the temperature of tobacco, the differential in temperatures of gas prior and subsequent to passage through tobacco will be zero, independently of the amounts of gas which are caused to traverse the tobacco. This feature can be utilized for determination of tobacco temperature by continuously varying the temperature of inflowing gas until the detectors 24, 28 indicate the same temperature, i.e., the apparatus can be operated in such a way that a cycle is completed when the differential in temperatures determined by the detectors 24, 28 is reduced to zero. The temperature indicated by either of the two detectors is then the temperature of tobacco.

However, the just outlined apparatus is considered to be less practical than the apparatus which is shown in FIG. 1 because it requires at least some changes in temperature of inflowing gas before the two detectors will furnish identical measurements. It is much simpler to convey through a batch of tobacco (whose weight is known) a predetermined amount of gas and to measure the temperature of gas prior and subsequent to passage through the batch. By knowing the weight of the batch and the quantity of testing gas, it is a simple procedure to calculate the tobacco temperature on the basis of the differential between the values furnished by the two detectors. As a matter of fact, the detector 24 may be dispensed with if the temperature of gas entering via supply pipe 22 is known and remains constant.

In treatment of many types of tobacco, accurate determination of the average temperature of successive increments of a tobacco layer or stream is particularly important immediately after heating and prior to subsequent cooling of tobacco. In this way, the operators will be able to properly select the extent and duration of the cooling action in order to reduce the temperature of tobacco to a desired value. As a rule, tobacco is cooled with air which is being caused to flow through successive increments of a travelling tobacco layer. Thus, and since the cooling treatment necessitates the passage of a cool gas through the tobacco mass, it is of particular advantage to utilize such cooling fiuid as a means for rapidly determining the average temperature of successive increments of the tobacco mass. In other words, the determination of tobacco temperature is then incidental to a desired cooling action, or vice versa. As stated before, the operation could be carried out in such a way that a current containing a predetermined quantity of gas would be caused to pass through a first batch of tobacco in the chamber 8, that a second quantity of gas would be caused to pass through a second batch which has been introduced into the chamber 8 subsequent to evacuation of the first batch, and so forth. However, and since all or nearly all tobacco processing apparatus utilize one or more conveyors which advance tobacco from station to station in the form of a continuous stream, it is desirable to determine the temperature of successive tobacco increments in a continuous operation, i.e., not in stepwise fashion. Thus, and as described in connection with FIG. 1, Burley tobacco is relieved of nitrogen in a continuous operation by heating successive increments to requisite temperature, by subsequent cooling and, if necessary, 'by moistening if the heating operation resulted in expulsion of excessive amounts of moisture. Moisture cannot be introduced into hot tobacco because it will evaporate immediately; therefore, Burley tobacco is first heated to bring about expulsion of nitrogen and is thereupon cooled to a temperature at which it can readily take up requisite amounts of moisture such as are needed to insure satisfactory treatment of tobacco at one or more further processing stations. By placing the detectors 24, 28 into the current of air which is utilized to cool Burley tobacco on its way from the drying to the moistening station, I insure that the dimensions of the apparatus are not increased for the sole purpose of properly determining the temperature of successive increments. Furthermore, such mounting of the detectors 24, 28 insures that the pneumatic cooling system may be used for accurate determination of the average temperature of successive increments of the tobacco stream without necessitating the provision of additional blowers, conduits and other auxiliaries which are needed to convey a gas through a travelling body of fibrous material. Still further, by providing an operative connection between the detectors 24, 28 and the heater 14 of the unit 11, I insure that tobacco passing through the chamber 6 is invariably heated to a temperature which is high enough to effect satisfactory expulsion of nitrogen but is not excessive so that the heating step does not result in expulsion of unwarranted amounts of moisture.

FIG. 2 illustrates a portion of a modified apparatus wherein the parts are denoted by reference numerals similar to those used in FIG. 1. The temperature of the current of cooling gas is measured only in that portion of the cooling chamber 108 which is first to receive successive increments of the tobacco stream 103 from the drying chamber 106. The chamber 108 is provided with a partition 105 which subdivides its interior into two compartments or ducts 107, 107a. The detectors 124, 128 are disposed in the measuring duct 107. The remaining parts of the apparatus are identical with the corresponding parts of the apparatus shown in FIG. 1. The inlet 122 extends along the full lower end of the chamber 108 to admit cool atmospheric air or another gas which is drawn upwardly by the fan 133. It will be seen that the major part of cooling air bypasses the detectors 124, 128 and flows directly into the discharge pipe 126 of the pneumatic unit 109, i.e., the detectors measure only the temperature of that small portion of the ascending air current which flows through the duct 107 and passes through the tobacco stream 103 immediately after the latter enters the cooling chamber 108. In other words, the detectors 124, 128 determine the temperature of cooling air which passes through a very hot portion of the tobacco stream. The differential in temperatures determined by the two detectors is an accurate indicator of thetemperature and moisture content of tobacco which leaves the drying chamber 106.

FIG. 3 illustrates a portion of a third apparatus wherein the parts are denoted by reference numerals similar to those used in FIG. 2. The main difference between the apparatus of FIGS. 2 and 3 is that the measuring duct 207 conveys a current of cooling gas which is drawn upwardly by a separate adjustable blower or fan 215. The fan 233 draws the main current of cooling gas which ascends through the duct 2070. The provision of a separate fan 215 for the duct 207 renders it possible to regulate with greater accuracy the rate of flow of that current of cooling gas whose temperature is measured by the detectors 224, 228.

An important advantage of the apparatus shown in FIGS. 2 and 3 is that they insure more accurate determination of the tobacco temperature. This is due to the fact that the detectors 124, 128 or 224, 228 need not measure the average temperature of the entire gas current which passes through the chamber 108 or 208 but only the average temperature of a small fraction of such gas current. It is well known that even strong agitation will fail to equalize the temperature in all zones of a relatively wide gas current, i.e., the provision of sieves 30, 32 might not be sufi'icient to insure that the detectors 24, 28 of FIG. 1 will invariably furnish readings which are truly representative of the average temperature of gas which is drawn by the fan 33. On the other hand, it is not important that the detectors 24, 28, 124, 128 or 224, 228 should determine the average temperature of a relatively large gas current because the determination of tobacco temperautre can be carried out with equal (and normally higher) accuracy if the cross-sectional area of the measured current is relatively small. All that counts is that the current of gas ascending through the duct 107 or 207 should traverse a portion of the tobacco stream 103 or 203 which is sufficient to insure satisfactory rise in temperature of the gas current so that the detectors 124, 128 or 224, 228 will furnish readings which are different. The difference between the readings furnished by such detectors will be greater if the duct 107 or 207 is immediately adjacent to the wall which separates the chamber 108 or 208 from the chamber 106 or 206. While FIGS. 2 and 3 show that the ducts 107, 107a and 207, 207a are fully separated from each other by the provision of partitions 105, 205 which permit the passage of upper and lower stringers of the belt 104 or 204 and of the tobacco stream 103 or 203 but substantially prevent communication of gases between the respective ducts, such substantially total separation of gases in the two compartments is not absolutely necessary. Thus, it is often sufficient to install in the chamber 108 or 208 suitable bafiles which will prevent thorough intermixing of the main body of the ascending gas current with that portion of the ascending current whose temperature is determined by the detectors 124, 128 or 224, 228.

Instead of utilizing a variable-delivery fan 133 or 215, the apparatus of FIG. 2 or 3 may be provided with suitable valves which can regulate the rate of gas flow through the duct 107 or 207. Furthermore, each of the three illustrated apparatus preferably comprises suitable flow meters which can determine and indicate the rate of gas flow through the chamber '8, duct 107 or' duct 207. Such flow meters are well known in the art and need not be shown or described here.

The detectors of the apparatus shown in FIGS. 1, 2 and/or 3 can be replaced by devices which determine changes in another physical property of the gas current, for example, by moisture detectors so that the differential in moisture content of the gas prior and subsequent to its passage through the tobacco stream will be indicative of the moisture content of tobacco. Furthermore, such differential can be utilized for convenient calculation of the tobacco temperature. However, and when the tobacco is Burley, drying of such tobacco brings about changes in temperature which are sufliciently proportional to changes in moisture content so that the determination of tobacco temperature can be used to calculate the moisture content.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. Apparatus for determining the temperature of tobacco, comprising foraminous conveyor means arranged to advance a stream of tobacco at a substantially constant rate in a predetermined path; pneumatic means for passing a current of gas transversely through said predetermined path and through successive increments of tobacco in a pre-determined portion of said path so that tobacco exchanges heat with the gas transversely passing therethrough; and measuring means for determining the difference in gas temperatures prior and subsequent to passage of gas transversely through the tobacco stream, said measuring means including a first temperature measuring device located in the gas flowing towards said portion of said path and a second temperature measuring device located in the gas flow which has passed transversely through the tobacco stream.

2. Apparatus as defined in claim 1, wherein said first and second measuring devices comprise a first detector located in the current of gas at one side of said predetermined portion of the path to determine the gas temperature prior to exchange of heat with tobacco and a second detector located in the current of gas at the other side of said predetermined portion to determine the gas temperature subsequent to exchange of heat with tobacco.

3. Apparatus as defined in claim 1 wherein, prior to passing through the tobacco stream, the temperature of said gas is lower than the temperature of tobacco so that said exchange of heat results in cooling of tobacco.

4. Apparatus as defined in claim 1, wherein said pneumatic means comprises a plurality of ducts for passage of said gas current through the tobacco stream and wherein said measuring means comprises a first detector located in one of said ducts at one side of said predetermined portion of the path to determine the temperature of gas prior to exchange of heat with tobacco and a second detector located in said one duct at the other side of said predetermined portion to determine the temperature of gas subsequent to exchange of heat with tobacco.

5. Apparatus as defined in claim 4, wherein successive increments of tobacco are conveyed first across said one duct.

6. Apparatus as defined in claim 1, wherein said pneumatic means comprises distributing means for distributing the gas uniformly in each increment of said predetermined portion of said path.

7. Apparatus as defined in claim 1, wherein said pneumatic means comprises two ducts for the passage of said gas current through said predetermined portion of said path and wherein said measuring means is provided in one of said ducts.

8. Apparatus as defined in claim 7, wherein said pneumatic means comprises separate blower means for forcing the gas to flow in said one duct.

9. Apparatus as defined in claim 1, wherein the tobacco in said stream contains nitrogen and further comprising heating means arranged to heat successive increments of said tobacco stream in a second portion of said path which is located upstream of said predetermined portion to a temperature high enough to effect expulsion of nitrogen prior to exchange of heat with said current of gas, the temperature of tobacco entering said predetermined portion being higher than the temperature of said gas current so that the exchange of heat results in cooling of tobacco.

10. Apparatus as defined in claim 9, further comprising wetting means disposed downstream of said predetermined portion of said path for raising the moisture content of successive increments of said tobacco stream.

11. Apparatus as defined in claim 9, further comprising control means for varying the heating action of said heating means as a function of the diflerential between the temperatures of said gas current prior and subsequent to exchange of heat with tobacco.

References Cited UNITED STATES PATENTS 2,086,194 7/1937 Smith 13l136 2,105,848 1/1938 Touton 131135 X 2,768,629 10/1956 Maul 131-136 X 3,224,452 12/1965 Franklin et a1. 131136 X FOREIGN PATENTS 875,684 8/1961 Great Britain. 947,280 1/ 1964 Great Britain.

SAMUEL KOREN, Primary Examiner I. H. CZERWONSKY, Assistant Examiner US. Cl. X.R. 131-136, 121 

